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Teen girls have their teen growth spurt at an earlier age than boys, and thus reach their adult height earlier, says the Institute for Arthroscopy and Sports Medicine (IASM). Teen girls have more body fat than teen boys, because of higher estrogen levels. Teen boys have more lean body mass because of higher androgen levels. Teen girls, even after weight training, have less upper body strength than teen boys.

Estrogen's role

Estrogen appears to affect a female athlete's ligaments, making them more relaxed and boosting the risk for injury, the IASM says. The anterior cruciate ligament (ACL) in the knee seems particularly vulnerable because of this, especially at certain times during a teen girl's menstrual cycle.

Physical differences in teen girls also affect the ACL and the knee, in general. There is less space in a teen girl's knee for the ACL; this puts more stress on the ligament, making it easier to tear, the IASM says. Teen girl athletes also use their quadriceps muscles (on the front of the thigh) more than their hamstrings (at the back of the thigh). The hamstring muscle provides most of the protection for the ACL, so weaker muscles can make injury more likely. Teen girls have wider hips than teen boys, and this difference in width puts more stress on the knees, particularly when landing from a jump. When a girl lands, she has more flex in her ankle and more foot roll out.

The highest-risk sports for ACL injury include: basketball, soccer, cheerleading, field hockey, singles tennis, lacrosse, and skiing. According to the American Academy of Orthopaedic Surgeons, the incidence of ACL injuries is estimated at nearly 200,000 each year.

In addition to knee injuries, teen girls may be more likely to have problems with shoulder instability and ankle sprains because of more lax ligaments.

Reducing ligament injuries

Here are several suggestions for teen athletes:

Strengthen leg muscles, particularly the hamstrings.

Learn how to land properly after jumping, with knees bent and hips flexed forward.

Strengthen core muscles in the trunk, hips, pelvis, abdomen and back.

Warm up before beginning any activity, take rest breaks, and cool down and stretch after play. The National Athletic Trainers' Association also suggests cross training, rather than overusing the same muscles by playing the same sport constantly.

Breast problems

Teen girl athletes may also have breast pain and discomfort because of friction, lengthy periods of motion and, depending on the sport, injury from a blow to the breast, the IASM says.

One of the best ways to prevent breast injury caused by motion and friction is to wear a well-fitting sports bra. The sports bra should limit breast motion as much as possible and be made of breathable fabric.

For teen girls who run or participate in other sports with repetitive running, the nipples may become irritated. Cold wind can worsen the irritation. A well-fitting sports bra can reduce nipple injury. Petroleum jelly or Band-aids may also help.

Anabolic steroids

Although most high school girls don't use anabolic steroids, studies have found that up to 2.5 percent of them have tried these illegal substances to boost athletic performance, the IASM says.

These are the side effects teen girls can experience when using anabolic steroids: